Interactions between normal human mammary epithelial cells (HMECs) and extracellular matrix (ECM) are critical for maintaining normal mammary gland homeostasis and loss ECM-signaling is observed during early mammary carcinogenesis. During the original funding period of this grant, we tested the hypothesis that 1) ECM-mediated growth regulation signals target the elimination of acutely damaged HMECs and 2) loss of ECM-signaling may provide a local environment or "high-risk epithelial field" that promotes the survival of a second genetic "hit". We identified an important role for the CREB-binding protein, CBP, in regulating apoptosis in HMECs that had acutely lost p53 function (*p53(-)HMECs). CBP promoted apoptosis in conjunction with 1) loss of CBP phosphorylation at Thr1871, 2) recruitment of CBP to the interferon regulatory factor-1 (IRF-1) GAS element, and 3) induction of IRF-1. These observations suggest that CBP acts to target the elimination of HMECs that have acutely lost p53 function and loss of CBP expression may provide an environment that promotes the survival of a second genetic "hit". Random Periareolar Fine Needle Aspiration (RPFNA) is a research tool developed to test for "high-risk" epithelial field effects in women at high-risk for breast cancer. In Preliminary Data, we used RPFNA to show that loss of CBP predicted atypia in mammary epithelial cells but only in specimens that expressed low levels of ER. Based on these observations, we will test the hypothesis that 1) CBP targets the elimination of acutely damaged p53(-) HMECs through recruitment of CBP to the IRF-1 GAS-element and 2) in high-risk women that loss of CBP promotes ER(-) mammary carcinogenesis. Aim I will test whether loss of CBP phosphorylation at Thr1873 promote apoptosis in *p53(-)HMECs through recruitment of CBP to the IRF-1 GAS-element enhanced affinity of the CBP CHS domain for STAT1 and 2) recruitment of CBP to the IRF-1 GAS element. Aim 2 will test whether the survival factor Akt regulate phosphorylation of in vitro and in vivo phosphorylation studies of tryptic digests of either expressed or isolated CBP by HPLC-TOF-MS. Aim 3 will test whether loss of CBP in high-risk women predict ER(-) cytological progression. Significance: Completions of these aims will provide insight into early events in ER(-) mammary carcinogenesis and provide novel targets for breast cancer chemoprevention. [unreadable] [unreadable] [unreadable]